1. Field of the Invention
This invention relates generally to an objective lens driving apparatus, and more particularly to such apparatus which is adapted to drive an objective lens for converging a light beam emitted from, for example, a light source on the signal recording plane of an optical disc in the focus direction and tracking direction or in one of these directions.
2. Description of the Prior Art
There have conventionally been proposed an objective lens driving apparatus which is constructed such that a movable body to which an objective lens is attached is supported by a single supporting arm having a hinge and a parallel link on a base (see U.S. Pat. No. 4,766,583) and another one which is constructed, as shown in FIG. 1, such that a bobbin 4 supporting an objective lens 1 and having a driving coil 2 for focusing control and a driving coil 3 for tracking control is disposed between magnets 6 arranged opposite to each other on a base 5 which serves as a yoke and supported in a cantilever manner by supporting rods 8 made of metal having resiliency and respectively fixed to upper right, upper left, lower right and lower left portions of the front surface of a fixing plate 7 implanted on the base 5 such that they are in parallel to each other in a cantilever manner.
In the latter one, the bobbin 4 is moved by the resilient displacement of the supporting rods 8 which is caused by supplying a driving current to the driving coil 2 for focusing control or the driving coil 3 for tracking control and consequently the objective lens 1 supported by the bobbin 4 is moved on the basis of a focusing error signal or a tracking error signal in the focusing direction (the direction of the optical axis of the objective lens 1 or the direction parallel to the optical axis) or the tracking direction (the direction perpendicular to the optical axis of the objective lens 1 or the plane direction perpendicular to the optical axis).
The former of the above-mentioned prior art devices, that is, the objective lens driving apparatus as disclosed in U.S. Pat. No. 4,766,583, has the hinge of the supporting arm positioned at the rotating center of the movable body, which causes restriction to the form of the movable body. For example, the freedom in the location of the optical system is decreased when the apparatus is integrally driven, consequently presenting difficulties on making the apparatus thinner.
On the other hand, according to the latter one, that is, the objective lens driving apparatus as shown in FIG. 1, since it adapts a cantilever spring supporting system, the interval between the upper and lower resilient supporting rods is decreased as the apparatus is made thinner, thus presenting obstacles such as that the optical axis of the objective lens is readily inclined. Further, when it is integrally driven, it requires additional signal line lead-out method so that the construction is made complicated. Moreover, four resilient supporting rods do not allow setting the vibration characteristics independently to the focusing direction and the tracking direction, thereby incurring troubles such as that the operation lacks smoothness.